Welcome to the GBodyForum!
Your Monte looks to be in good shape. It's nice to see you getting on the little issues right away. That's what makes an "OK" car a nice car. There's plenty of cheap and easy things you can do to bring your ride to the next level. The 383 is always a good strong power plant if your looking to keep things "old school" looking. Just remember, you'll want to be sure your 200/4R will support the torque the 383 puts out. (ask me how I know) I went with a TH400 with mine as I still have freeway gears, but will switch to a 4 speed automatic once the rear end is replace with a bit more of a street gear.
You have joined a very good forum with a lot of knowledgeable guys (and gals) here to help with all of your questions. From mild to wild, we have it all.
Good luck with your build.